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View Full Version : Strange check engine light problem.... A/C related



Jareds 89 LX-i
03-04-2003, 09:42 PM
Alright this problem has got me stumped. I got my A/C fixed last week after it having it not working for about 3 years now. The A/C itself works GREAT (35 degrees! :D ), however, I keep getting a check engine light on certain occations. It ONLY comes on when the A/C is on, never when it's off. The first time I pulled the codes I got a code 6, which is engine coolant temperature sensor, but I believe that was an old code from when I had a wire break off one of the temp sensors. I pulled the clock/ECU fuse to reset it, and drove around for a couple more days. The light still came back on on several occations, so I went to pull the codes again tonight and there were no codes! Now the light usually only comes on when you're going slow, such as lots of traffic lights or stop signs, stuck in traffic, parking lots, etc. If I just get right on the highway and drive it won't come on at all. I used the a/c the entire time on my trip to Orlando the other day, and that was 3.5 hours there and 3.5 hours back, and the light never came on once, but as soon as I pull into a parking lot and drive slow for a couple minutes (on and off the gas/brake) there's Mr. CEL!

So here's what I'm starting to think. About 8-9 months ago, I had a wire running through my door which held the weatherstrip open a bit, and with the front of my car pointing slightly downhill, my entire drivers side floorboard flooded during a very heavy rainstorm (as in about 1-1.5 inches of standing water). I didn't realize it at the time, but the ECU was submerged in water, and caused the car not to start (so yes, it was turned on while underwater). After I got all the water out I took the front and back covers off the ECU and cleaned it off real good, and dried it with a hairdryer on the cool setting. This underwater ECU thing happened a total of 2 times before I figured out what was causing the flooding. Both times I put it back in and it's worked perfectly fine, no problems at all. But perhaps (just by luck) it damaged just a part of the ECU that deals with the A/C (???). I don't know if that's possible or not, but it's the only thing I can think of that kinda makes sense. Anybody think that's possible? Another ECU from the boneyard might be the way to go....

If anybody else had any other ideas on what might be causing this, please share! It doesn't affect driveablity one bit, or a/c. Everything works perfectly normal, cooling fans work just like they should, temp is fine, EVERYTHING'S PERFECT, just that annoying light! It goes off when you restart the car, but sometimes comes back on shortly after, and sometimes doesn't come on at all (depends on conditions listed above).

So anybody got any ideas? My cars brain ain't talkin!

cruznz
03-04-2003, 11:56 PM
i think no code indicates an ECU fault........only way to be certain is trying a known good one....

AccordEpicenter
03-05-2003, 12:32 PM
yeah the ecus can be damaged when they get wet but ive recovered 2 from cars that had flooded floors and both were pristine in the inside and corroded on the outside so you never know what youre gonna get until you look inside. Also when that happens the wiring harness and connectors tend to get fucked and corroded easily, thats what id check. Just take some white lithium grease and spray it into the connector and plug it in/take it out like 20x and you should be good...

meohmy01
03-05-2003, 12:43 PM
our cars have a check engine light?

88' Accord Ltd
03-05-2003, 03:30 PM
They do but only on the fuel injected models.

Jareds 89 LX-i
03-05-2003, 09:30 PM
Thanks for the info.... I'm gonna go at it with my testlight and voltmeter and try and figure out if there's a problem with the wiring or the ECU. My service manual gives a procedure for checking the sensor, as well as checking for voltage to the sensor from the ECU. The ECU itself and the connection going to it look fine from what I can tell, but I'll clean out the connector real good anyways. I'll find it eventually! hehe

Thanks again :)

Anybody have any other ideas to try?

ACCORD EX
03-06-2003, 03:54 AM
sorry i haven't read this post before ! but i don't think that our ECU's deal with A/C ! i know that new cars do ! but not in the 80's ! :)

not sure though !

AccordEpicenter
03-06-2003, 09:24 AM
yeah they do... controll alot of stuff like ac clutch and what not. I dont think it actually has any problem with his ac its probably a messed up ecu connector. Wierd things happen when those connections get messed

offthahook
03-06-2003, 10:00 AM
Hmmm... When I had my AC fixed after years of nonuse, the ECU hadda be replaced. Not the same situation as yours, but my AC idle increase thingy would not kick in when the AC was cut on. We don't know why, but the used ECM fixed it. I'm unsure as to which body styles you can interchange. If I were you, I'd get one from an 89 four door just to make sure it is a perfect match. Part numbers are on the unit in sticker form. Make sure they match or you will have issues

AccordEpicenter
03-07-2003, 10:55 PM
any FI computer will work...

Jareds 89 LX-i
03-20-2003, 09:33 PM
Well for anyone that might care, I think I got it all figured out. I got another ECU at the junkyard today (the right one this time!), and the light hasn't come on yet. I drove around alot tonight in the conditions that it usually always came on in (stoplights, going slow, parking garage, etc), and never once did it come on. I took the back plate off my old ECU, and look what I found!

http://www.hpphoto.com/servlet/LinkPhoto?GUID=7b752264-4f5d-2d0b-783d-46941f89105c&size=

It's kinda hard to see in the pic, but on the side with the rusty screws, the green circuit board is a totally different shade of green than the rest of it.... much lighter. There was also some clear stuff flaking off from it, so I'm gonna take a guess and say that was probably causing something in there to malfunction. There was also some corrosion on the pins in the connections as well. New one seems to work good though, so I think that's all it was.

AccordEpicenter, all the EFI ECU's are not the same. The first time I bought an ECU out of an 88 LX-i, and I later found out that the 88 EFI and 89 EFI are completely different ECU's (and to buy new from Honda, the 89 is about $300 more than the 88....weird). I know the 86-87 EFI ones aren't compatable at all since there's different sensors and other stuff, so I didn't even bother with those.

:)

ACCORD EX
03-21-2003, 02:01 AM
man ! first time i see and ECU ! thanx for sharing !

MIKE

Low Tek
03-21-2003, 06:37 PM
I am having a problem with the check engine light too... mine seems to come on at high rmp... did the test and it came up with a air flow sensor.. I replaced it, but it seems to still come on, and the gas miliage has gotten worse too.. any ideas??:wtf: